\documentclass{article}
\usepackage{amssymb,amsmath,amscd,concmath}
\pagestyle{empty}
\begin{document}
\begin{equation*}
  F(n)=
  \left\{
   \begin{matrix}
    0\,,\qquad\qquad\qquad\quad\,\ \ \,&&\mbox{if }n=0\,;\ \ \\
    1,\qquad\qquad\qquad\qquad\,&&\mbox{if }n=1;\ \ \,\\
    F(n-1)+F(n-2)&&\mbox{if }n>1.
   \end{matrix}
  \right.
 \end{equation*}
\end{document}
